linear decrease, followed by a knee and a plateau (6). The plateau value increases markedly with increasing height of observation in the flame. Obviously an interference effect of type I a is present here between calcium and aluminum. However, when Al(NO& is added, the calcium emission drops smoothly to zero with increasing aluminum concentration and depends hardly on the height of observation (6). An interference of type I I a has to be assumed to play a part here. It is well known that the presence of Al(N03)s in the solution leads to the formation of highly refractory particles in the flame. Occlusion of the analyte in such particles at relatively high aluminum concentrations explains the different behavior of calcium depression by Al-
(Nods. I n practice solute vaporization interferences may appear to be much more complicated than is suggested by our simple scheme above. Interference effects of both types I and I1 may occur in combination for a given pair of analyte and concomitante.g., in the case of calcium depression by Al(N0s)s. When more than two elements are present together in the solution, competition effects between their mutual chemical reactions in the aqueous phase should also be considered (2). Moreover, in turbulent flames with total-consump-
tion aspirator-burners (so-called atomizer-burners) these interference effects may appear to be smeared out and more capricious because of inhomogeneities in flame temperature and metal flame content and because of the nonuniform size distribution of the spray droplets. These complications might perhaps explain the occasional observation that a minimum in analyte emission as function of concomitant concentration is followed by a gradual increase or even a maximum of emission (3, 12). The remarkable observation with a turbulent atomizer-burner flame that the calcium depression by indium is relatively smaller at the base of the flame than at larger heights (3), which contrasts with the usual observation in (laminar) flames (6), might be explained by the incomplete evaporation of spray droplets a t the flame base. This incomplete evaporation is a well-known feature of this kind of flames with aqueous solutions (6) and as a consequence only the smaller droplets present in the spray will contribute to the formation of dry aerosol particles a t the flame base. Since a small droplet will naturally lead to the formation of a small aerosol particle and hence to a quicker vaporization, the resulting solute vaporization interference could appear to be less a t the flame base than at larger heights where grosser droplets contribute also.
LITERATURE CITED
(1) Dean, J. A,, “Flame Photometry,”
McGraw-Hill, New York, 1960. (2) Dinning, J. I., ANAL.CHEM.32, 1475 (1960). (3) Doty, M. E., Schrenk, W. G., “Developments in Applied Spectroscopy, Vol. 111, p. 196, J. E. Forrette and E. Lantennan, eds., Plenum Press, New York, 1964. (4) Gilbert, P. T. “Analysis Instrumentation-1964,” (Proc. 10th Natl. Anal. Instr. Symp., San Francisco, June 1964) Plenum Press, New York, 1964. (5) GuBdon, J., Voinovitch, I. A., Chem. Anal. Warsaw 5, 193 (1960). (6) Herrmann, R., Alkemade, C. Th. J., “Chemical Analysis by Flame Photometry” (transl. by P. T. Gilbert) Interscience, New York, 1963. (7) Konopicky, K. Schmidt, W., Z. Anal. Chem. 174, 262 (1960). (8) Margoshes, M., Vallee, B. L., ANAL. CHEM.28, 180 (1956). (9) Poluektov, N. S., “Techniques in Flame Photometric Analysis,” (transl. by C. N. Turton and T. I. Turton) Consultants Bureau, New York, 1961. (10) Pungor, E., Konkoly-Thege, I., Mikrochim. Acta 1959, 712. (11) Schmidt, W., Konopicky, K., Baum, M., Tonind.-Ztg. Keram. Rundschau 87, 157 (1963). (12) Strasheim, A,, Wessels, G. J., Appl. Speclry. 17, 65 (1963). (13) Wallace, F. J., Analvst 88. 259 (i963). ’ (14) West, A. C., ANAL.CHEM.36, 310 (1964). c. TH. J. ALKEMADE Physical Laboratory State University Utrecht, The Netherlands > - - - -
Radiochemical Determination of Cesium Using Permanganate as a Precipitant SIR: The reagents commonly used as the final precipitant in the radiochemical determination of cesium are perchloric and chloroplatinic acids (3, 4). The chemical yield in these procedures is determined by weighing the precipitated cesium salt and comparing this weight with the expected weight based on the amount of cesium initially added. However, if even small amounts of ammonia are accidentally introduced into the laboratory area and dissolved in these acids, an error in the estimate of the chemical recovery results because of the low solubility of the corresponding ammonium salts. Experience has shown that under normal laboratory conditions where ammonium hydroxide is used, the probability of accidental introduction of significant amounts of ammonia into the final stage of the cesium analysis is quite high. Other problems, in working with these reagents, are the hazards involved in using perchloric acid-ethanol mixtures and the difficulties of redissolving the chloroplatinate salts if flame photo-
metric techniques are to be used for chemical yield determinations. Also, cesium-131 tracer with its short half-life (9.7 days) has been used to determine the cesium chemical recovery when there is a probability of ammonium contamination ( 2 ) . This approach presents some difficulties with very low levels of cesium-137, since the x-rays of the cesium-I31 daughter (Xe131) contribute to the beta background. To obviate these problems of determining the cesium recovery, other precipitants were sought. Sodium permanganate was evaluated as a precipitant for cesium because other investigators (1) have found it to be a satisfactory precipitant. The direct weighing of cesium permanganate to determine the chemical recovery is precluded by the presence of manganese dioxide formed when a high concentration of permanganate ion comes in contact with extraneous oxidizable substances such as filter paper. However, the difficulties involved in determining the chemical yield are overcome by dis-
solving the cesium permanganate after counting and assaying the cesium by flame photometry. In the development of this procedure, the important parameters studied were the optimum ratio of cesium ion concentration to the amount of sodium permanganate added and the effect of different acids and their concentration on the flame emission. Once values of these parameters were fixed, a selfabsorption curve for the beta-ray counting of Csls7was constructed. EXPERIMENTAL
Reagents. Cesium chloride and sodium permanganate were Purified Grade from Fisher Scientific Co., Fair Lawn, N. J. Phosphoric acid, sulfuric acid, and sulfurous acid were Reagent Grade from J. T. Baker Chemical Co., Phillipshurg, N. J. A cesium chloride standard solution was prepared by dissolving cesium chloride in distilled water. The amount of cesium in solution was determined gravimetrically with chloroplatinic acid in an ammonia free atmosphere. The VOL. 38, NO. 9, AUGUST 1966 e
1253
completeness of the cesium chloroplatinate precipitation was established by isotopic dilution using cesium-137 as the tracer and then counting of the supernatant liquid t o determine the fraction of unprecipitated cesium. Cesium-137 tracer was obtained from Oak Ridge National Laboratory. Its absolute disintegration rate was determined by 4n beta counting. Instruments. A Beckman DU spectrophotometer with a flame attachment was used to assay for cesium. Procedure. The Drocedure described here starts af(er the cesium has been removed from the sample (for instance, seawater) and purified of possible interfering nuclides. Chloride ion, which reduces Mn04-, is removed from a purified cesium solution by the addition of 1 ml. of concentrated HzS04 and evaporation to fumes of so3. Then 10 ml. of water, 1 ml. of 85% HsP04, and 0.5 gram of KaMn04 are added in that order. After complete solution of the NaMn04, the solution is chilled in an ice bath. The resulting cesium permanganate precipitate is isolated by filtration. It is then dried, weighed (for selfabsorption, self-scattering correction) , mounted, and counted. After counting, the precipitate is dissolved with 5 ml. of concentrated and approximately 5 ml. of water containing 0.5 ml. of concentrated HzS04. When the precipitate is completely in solution, the filter paper is removed, rinsed, and discarded. The clear solution is evaporated to fumes of SO3, cooled, and diluted to 100 ml. Then the solution is submitted to flame analysis, using an oxygen-hydrogen flame, on the spectrophotometer. Cesium is determined a t 852 mp. Since both the beta-ray counting self-absorption and the per cent optical
Table I. Effect on Chemical Yield of Cesium of Amount of NaMnO4 Used Relative to Cesium
Stoichiometric ratio of NaMnO4 to Cs
Recovery of Cs, %
2 4
58.8 84.1 97.1
8
Table II. Quantities of MnOz in CsMn04 Precipitate Wt. of Wt. of
CsMnO4 and MnOz found, mg. 54.4 42.7 40.3 27.9 27.6
CsMnOd from flame Wt. of assay, mg. MnOz, mg. 53.2 40.9 37.9 26.0 25.6
1.2 1.8 2.4 1.9 2.0
X = 1.9 f 0.5 ~
1254
ANALYTICAL CHEMISTRY
-14
-20 -22 -24
-28 -2b
1 p.p.rn. X l o a . Effect of acids on flame analysis 0 HClOa, 0 Hzs04, A HCl
Figure 1 .
transmittance curves are linear for the conditions utilized, their equations can be derived and, for simplicity, combined. The equation for optical transmittance as measured by the flame photometer is T = CWrp D
+
The equation for self-absorption and self-scattering in the beta-ray counting of Cs137, neglecting the chemical yield correction, is d.p.m. -- AW, c.p.m.
+B
Because the chemical yield is W,/W,, the disintegration rate of CsI37 in the sample can be found by dividing the disintegration rate of Cs137 in the counting sample by the chemical yield, to give d.p.m.
=
c.p.m. (AW,
+ B ) )D?:(-
where A
B
= slope of self-absorption curve = intercept of self-absorption
C D
= slope of transmittance curve = intercept of transmittance
curve
curve
W, = weight of Cs;Cln04observed by W, W,
T
weighing weight of Cs added initially = weight of Cs used in construction of transmittance curve = per cent transmittance as measured by the flame photometer
=
RESULTS AND DISCUSSION
A study was made to adjust the important parameters to values which would give a large chemical yield, a high counting efficiency, and a high sensitivity in determining the chemical yield.
A significant factor in obtaining a large chemical yield is the ratio of permanganate to cesium concentration in the precipitating solution. Table I shows that if there is about an eightfold excess of a stoichiometric amount of NaMn04to Cs, the recovery of cesium is nearly quantitative. Since small amounts of hlnOz are precipitated along with the Csh!In04 precipitate, the cesium yield cannot be determined accurately by direct weighing. Table I1 shows that the quantities of MnO2precipitated are fairly constant even though the weight of CsMn04 varied by a factor of two. Since it is necessary to have an acidic solution to dissolve the CsMn04 after counting, a study was made of the sensitivity of the flame emission to the presence of HC1, HzSO4, and HC104. Figure 1 shows the per cent error in the cesium assay as a function of acid concentration. The long plateau exhibited by suggested the use of HzS04 in the procedure. The addition of 0.5 ml. of concentrated H2S04 to the sample and the subsequent evaporation to fumes of SO3leave the sample with an amount of HzS04that is on the plateau (Figure 1) but free of any possible interfering chloride ions. A calibration curve was constructed of the per cent flame transmittance as a function of cesium concentration. The results showed a linear relationship out to a concentration of 30 mg. of Cs per 100 ml. of solution. The calibrations were made a t a wave length of 852 mp, a slit width of 0.1 mm., an oxygen pressure of 10 lb./sq. inch, and a hydrogen pressure of 4 lb./sq. inch. A curve to correct for physical geometry and the scattering of the cesium
beta-rays was constructed by precipitating known amounts of Cs137 with various known weights of CsMn04. The counting rate on the low-background counter used in these studies can thus be corrected for geometry, self-absorption, and self-scattering to obtain the Cs137 disintegration rate. This curve showed a linear relationship over the weight range of 25 to 55 mg. of precipitate. The method presented for obtaining a cesium precipitate in a satisfactory form
for counting and chemical yield determination has eliminated the problem of ammonia interference. This method is currently being used successfully in a procedurc! to determine activity levels of C P 7 as low as 1 d.p.m. (total) from 55liter samples of seawater. LITERATURE CITED
(1) Caley, E. R., Deebel, W. H., ANAL. cHEM. 33, 309 (1961). (2) Noshkin, V. E., Woods Hole Ocean-
ographic Institution Rept. NYO-217433, NY0-3145-5, (lgfj5)* (3) ROCCO, G. G., Borecker, W. S., J. Geophys. R ~68,~ 4501 , (1963). (4) Sugihara, T. T., James M. I., Troianello, E. J., ANAL. HEM. 31, 44 (1959).
H. SHIPMAN WILLIAM DAVIDMUELLER
Applied Research Branch U. S. Naval Radiological Defense Laboratory San Francisco, Calif. 94135
Determination of Deuterium Ion Concentration in Dilute Unbuffered Deuterium Oxide Solutions SIR: This work concerns the determination of deuterium ion concentration in the DzO that serves as coolant and moderator in the nuclear reactors of the Savannah River Plant. To minimize corrosion of aluminum components during reactor operation, the DzO is maintained at a p D of 5 with nitric acid. Determination of the pD of this dilute solution is difficult because it is unbuffered. Routine in-line measurements by electrical conductivity are nonspecific and in-line measurements by pH meter with glass and calomel electrodes were not always satisfactory. Three laboratory methods for determination of acidity were investigated : conventional potentiometric measurements with glass and calomel electrodes, conductometric titration of the acid with base, and colorimetric determination of p D with an acid-base indicator. I n the colorimetric method, which comprises the bulk of this communication, conventional pH indicator colorimetry (1) was adapted to DzO solutions, and indicator constants for bromophenol blue (BPB)and bromocresol green (BCG) in DzO were determined by a method that did not require standard buffer solutions. Contrary to their customary usage, these indicators were employed as onecolor indicators. EXPERIMENTAL
Reagents. The BPR (Eastman Organic Chemicals, No. 752) was used as received; the BCG (Matheson Coleman & Bell, No. NB114) was recrystallized first from glacial acetic acid and then from benzene. The acid forms of the indicators were dissolved in deionized HzO or DzO to give 4 . 0 2 % solutions. The molarity of the indicator solutions was ealculated from the weight of indicator dissolved and confirmed by conductometric titration with base. Adjusted indicator for pH or p D determinations was made by neutralizing the solution of the indicator acid
0
0.1
0.2 ml. 0.01 N NaOH
0.3
Figure 1. Examples of conductometric titration curves of 1 O-5N nitric acid in HzO and DzO
until pH or pD equalled pK. I n the present application, for example, where BPB was used to determine pD of reactor moderator, the BPB was neutralized to a pD of 4.62; the pH meter was calibrated with the DzO buffer of pD 5.23 @),and HzO glass and calomel electrodes were used. Procedure. All measurements were made a t room temperature, -24' C. pD MEASUREMENT.Adjusted BPB indicator (100 pl.) was diluted to 25 ml. with sample solution; another 100 pl. were diluted similarly with 0.05M NazCOs. The absorbance of each solution was determined spectrophotometrically at 592 mp with a 50-mm. path length. DETERMINATION OF K. Absorbances of solutions of indicator acid at known concentrations in freshly deionized HzO or DzO and in 0.05M NazCOs were measured at wavelengths of 592 mp
for BPB and 615 mp for BCG. The ratio of the absorbance of the sample to that of Na2CO3 solution was defined as CY, the fraction of the indicator converted to the base form. DISCUSSION
Potentjometric Measurements. Measurements in lO+N acid solutions by a pH meter with glass and calomel electrodes generally gave values that were high. Results were similar, whether the solutions were made in HzO or DzO, or whether electrodes with HzO or DzO internal solutions were used. Satisfactory results were obtained with 10-4~solutions. The cause of the high results is unknown; perhaps some of the acid reacted with the glass. Potentiometric measurement of pH in dilute unVOL. 38, NO. 9, AUGUST 1966
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